A diesel, with its characteristics of low fuel consumption and high power ratio, is more and more widely applied. However, as nitrogen oxides of NOX generated in a cylinder of a diesel engine under high temperature and high pressure has brought serious environmental problems and exacerbates the deterioration of air quality, China has improved the emission standards for road vehicles with the diesel engine, currently, in terms of purifying diesel vehicle exhaust of NOX, Selective Catalytic Reduction (SCR) technology is mainstream technology, a urea-SCR system is most widely used, its principle is that a certain percentage of urea solution is injected at the front end of an SCR catalytic converter, ammonia produced by urea hydrolysis or pyrolysis is taken as a reductant to selectively reduce NOX at catalyst surface, however, the development of its core component of the SCR catalytic converter has a great shortage, i.e., when a vehicle is idling or under under-speed conditions, the exhaust temperature is mostly below 200° C., in such case, the conventional vanadium-titanium-tungsten type SCR has the temperature window of 280° C.-400° C., which cannot meet the requirement of NOX purification at low temperature. Meanwhile, long-term and heavy use of precious metals, particularly the use of vanadium, not only causes high production cost and environmental pollution, but also has a very serious damage to the human body.
Therefore, the development of SCR catalyst, which is more adaptive to low temperature and high conversion rate and is environmentally friendly, is the direction which the catalyst industry has been trying to explore.